The decomposition of aqueous solutions of chloroacetic acid in acid and neutral solutions by H atoms was investigated. The rate constants for hydrogen and chloride abstraction from the chloroacetic acid and from the chloroacetic anion by H atoms were derived. It was found that H atoms as such react with chloroacetic acid mainly by hydrogen abstraction. The comparison of these results with radiation chemical data yields evidence for the nature of the reducing radicals produced in the radiolysis of water. The acid form of these reducing radicals involves the H atom as such.